The present invention relates generally to an apparatus for the application of a coating material to a filament, such as, for example, a wire or optical fiber. More particularly, the present invention relates to cross-head die assemblies for the application of a coating material to a filament.
Cross-head die assemblies are used in applying a coating material, such as, for example, molten plastic, to a substantially continuous filamentary element. Cross-head die assemblies generally include a die member and a tip. The die member is an elongate frustoconical body that defines an axial bore therethrough. The die member is received within and is held by a die holder. The tip is placed into operable relation with, such as, for example, received within, a tip holder, and both are received within the die holder such that the tip is axially-spaced relative to the die member. The tip also defines an axial bore therethrough. The tip holder, or core tube, functions to ensure an even flow of coating material around the tip and into the space between the tip and the die member to thereby ensure an even distribution of coating on the filamentary member. The filamentary member is drawn axially through the axial bore in the tip. The tip functions to guide the filamentary element and establish a consistent axis of pull for the filamentary element. The draw of the filamentary element continues in an axial direction from the tip into and through the coating material contained within the space separating the tip and the die member. The filamentary element is then drawn axially through the die orifice in the die member. The difference between the diameters in the die orifice and the filamentary member determines the thickness of the coating material applied to, or remaining on, the filamentary element. Thus, the die orifice meters or removes coating material from the filamentary element.
In some crosshead die assemblies, the axial bore of the die holder is variously tapered. The outer surface of the die member is tapered to correspond to a particular section of the tapered axial bore of the die holder. When inserted into the tapered axial bore of the die holder, the corresponding taper of the die member acts to establish and maintain axial alignment of the components relative to each other. Similarly, the axial bore of the tip holder and the corresponding taper of the axial bore of the die holder cooperate to establish and maintain axial alignment of the components relative to one another.
Axial alignment of the crosshead die components and the filamentary element is critical in the process of applying a coating of material to a filamentary element. More particularly, axial alignment of the filamentary member and the die orifice is critical to producing a consistent thickness of coating material around the circumference of the filamentary element. As the filamentary element is drawn axially through the tip, friction between the wire and tip results in wear and degradation of the tip. Furthermore, typical coating operations, such as, for example, wire coating, run at speeds well in excess of one-thousand feet of wire per minute. Such pull speeds contribute to additional friction and the buildup of heat in the tip. The wear and tear on the tip permits the wire to depart from concentricity with the die orifice, thereby resulting in a loss of axial alignment of the wire relative to the die orifice, a decrease in the quality of the coating layer and, thus, a decrease in the useful life of a tip. Once the tip has incurred a certain degree of wear and tear, and thus a reduction in its ability to maintain the filamentary member in concentric relation with the die orifice, the tip must either be used for the application of coating layers which do not require tight tolerances or concentric coatings, or the tip must be remachined or recycled.
In order to reduce the frictional wear of the tip and increase the useful life thereof, hardened inserts have been variously placed in relation to the tip. These inserts generally are ring-shaped members and include a central bore through which the filamentary member or wire is drawn. Such inserts are typically placed anywhere from the rear of the tip holder to the outside surface of the tip itself, and are permanently affixed to the tip or tip holder such that the central bore of the insert is substantially concentric with the filamentary axis of pull. Alternatively, the die assembly may include a tip having two or more parts, or of multi-piece construction. The hardened insert is disposed between the tip pieces, which are then attached together, such as, for example, by welding, brazing, or threading engagement.
The process of affixing the insert to the tip introduces a new set of challenges and inefficiencies. If the insert itself is welded or brazed to the end of the tip, the diameter and thickness of the insert increase the nose diameter of the tip. The increased tip nose diameter results in the tip being spaced farther away from the die member, thereby reducing the quality and concentricity of the applied coating. If the insert itself is welded or brazed to the tip at any location other than the end of the tip, the problem of increased tip nose diameter is eliminated. However, the high temperature of the welding and/or brazing process may result in property changes, cracks or other degradation in the insert.
If the insert is constructed of a material that is not easily welded or brazed, or otherwise affixed to the tip, the insert may be accommodated within a tip having two or more pieces. For example, the insert can be sandwiched between the two tip pieces, which are then attached together by welding or brazing. However, the insert is still subjected to the heat from the welding or brazing process which potentially results in property changes, cracks or other degradation in the insert. If the insert is sandwiched between two tip pieces which are then threaded together, maintaining the critical alignment of the central bore of the insert with the axis of pull of the filamentary element is tenuous, and often compromised during, for example, assembly, cleaning or disassembly.
Therefore, what is needed in the art is a tip having increased resistance to wear and tear due to friction.
Furthermore, what is needed in the art is a tip that does not require remachining or recycling after its useful life has expired.
Even further, what is needed in the art is a tip that includes a hardened insert that has not been damaged or the properties thereof altered due to exposure to the high heat of welding, brazing or other attachment processes.
Still further, what is needed in the art is a tip that includes a hardened insert that remains in a substantially concentric relation with the filamentary member axis of pull during assembly, disassembly and cleaning.
Yet further, what is needed in the art is a method of attaching an insert that does not require welding or brazing of the insert to the tip.
Lastly, what is needed in the art is a method of attaching an insert to a tip without the need to expose the tip to the high heat of a welding, brazing or other attachment process.
The present invention provides a tip assembly for use with a cross-head die assembly.
The present invention comprises, in one form thereof, a tip having a nose portion. The tip defines a central bore. The nose portion includes a lip portion and defines a counterbore. The counterbore has a counterbore side wall and a seat surface. The counterbore is contiguous with the central bore. An insert member includes an inner surface, an outer surface and a side wall. The inner surface is opposite the outer surface. The side wall interconnects the inner surface and the outer surface. The insert defines a central aperture that extends from the inner surface to the outer surface. The insert is disposed within the counterbore such that the central aperture is substantially concentric with the central bore of the tip. The lip portion of the tip engages the outer surface of the insert.
An advantage of the present invention is the tip assembly has an increased resistance to wear and tear due to friction.
A farther advantage of the present invention is remachining or recycling of the tip due to wear and tear is not required.
A still farther advantage of the present invention is that neither the insert or tip is exposed to the high heat of welding, brazing or other attachment processes during assembly.
An even further advantage of the present invention is alignment of the insert with the filamentary member axis of pull is not compromised by assembly, disassembly or cleaning.